The present invention relates to a device for the protection of optical disc media such as CD- Audio, CD-ROM, CD-R and DVD, referred to herein collectively, but without limitation as "optical discs," CD refers to compact disc. The terms disc and disk are use herein interchangeably. A standard CD disc has a diameter of approximately 120 millimeters (mm), a thickness of approximately 1.2 mm and a weight of approximately 14-33 grams and a center hole diameter of approximately 15 mm. A standard CD disc is constructed of a layer of reflective aluminum or gold situated on a clear polycarbonate disc base. The base layer of the polycarbonate is stamped with small indentations referred to as "pits." A standard CD has a space approximately 1.5 mm in width at the outer and inner edge surrounding the area where data is stored. The top polymer layer of polycarbonate covers the opposite side of the aluminum layer and is referred to as a "lacquer." A standard CD player shines a laser beam through the polycarbonate and reflects the laser light off of the aluminum layer. The pits permit the variations in the reflected laser light to be interpreted as binary code. A CD-R compact disc drive works in a similar manner, except that the pits are formed in a layer of dye rather than in the polycarbonate layer and that a layer of gold is substituted for the reflective aluminum layer. In each case the optical transmission reflection of the optical disc clarity of the laser light is of paramount importance to the efficient operation of the disc and its player.
Optical discs are often packaged with rectangular plastic cases commonly referred to as "Jewel Boxes" or "Jewel Cases." The optical disc must be removed from these cases prior to insertion and play in the disc player, thus exposing the optical disc to damage, such as scratching or accretion of dirt or foreign matter. The present invention provides a protective covering which may be applied and removed without damage or alteration of the optical disc, but which need not be removed prior to use of the optical disc in its player. The present invention differs fundamentally and significantly in its design and purpose from Jewel Box type cases. The present invention also differs significantly in concept and design from cartridge type disc cases and mechanisms in which an optical disc is inserted into a fixed cartridge in which the disc spins, but the cartridge remains relatively fixed within the player.
The prior art also discloses protective covers comprised of protective sheets which are attached to the optical disc throughout adhesive strips or rings such as in lijima's U.S. Pat. No. 4,879,710. However, as noted by Burroughs in the UK Patent Application No. GB 2,279,799A such an invention is likely to permit air to be trapped between the disc and the covering such that differences in refraction could cause read errors in the playing mechanism. The Burroughs Application also discusses European patent Application No 0 300 733 A1 which uses a heat shrink process to cover the optical disc. Burroughs notes the possible damage to the disc from the heating process and the difficulty of application by non-experts. Also disclosed in the Burroughs Application is British Patent Application No. 2 217 507 A which utilized a protective shield applied to the non-read side of the disc through the use of adhesive gum and an external applicator device. The Burroughs Patent Application itself seeks to resolve these short comings by proposing the use of a protective shield assembly with a uniform coating of fluid adhesive material or refractive index matching liquid with that of the disc itself. Burroughs proposes to construct the shield casing from polycarbonate or acrylic resins. Burroughs also requires the imposition of a protective ring around the periphery of the optical disc, purportedly to protect the disc, but more obviously required to keep the fluid from escaping and damaging the disc.
The drawbacks of the Burroughs system are numerous. The fluid is likely to become contaminated during application thereby interfering with the laser's ability the read the pits in the disc. In addition, the fluid is likely to escape during high-speed rotation of the disc causing damage to the player. Burroughs also fails to provide any increased measure of protection from damage or scratching, since the shield would be made of the same substance as the outer layer of the disc. The reflective rim proposed by Burroughs supposes yet another component which is likely to come loose during disc play and is likely to damage the player and the disc if spun off during high speed rotation.
U.S. Pat. No. 5,757,765 to Chen seeks to overcome the short comings of lijima and Burroughs through the use of an annular adhesive sheet with a peelable releasing sheet, and radially extending ribs, through which the disc shield is attached to the inner portion the optical disc surface. The shield itself is referred to as a film with a thickness smaller than sixty micrometers. Such a device does not address the tendency of the sheeting to vibrate and pull away from the optical disc in places where the adhesive radial ribs are not affixed or where they have become worn. The Chen device also does not provide a substantial layer capable of protecting the disc from scratches by other objects, but rather supposes a film type sheet with minimal protective quality is similar to a dust cover.
U.S. Pat. No. 5,787,069 to Lowe, et al. discloses a disc cover (trademarked as CD ARMOR) with clasps along the outer edge to hold the cover together. The clasps are likely to hold poorly and tend to be uneven with hand assembly. This design is subject to warping especially when the edges are folded in the applicator disclosed by Lowe, et al. in U.S. Pat. No. 5,912,875.